Can cotton fin fungus affect other fish in the tank?

Fungus is not an infectious disease. What you have is a "bad water" problem possibly combined with a bit of fin nipping if the fungus is forming only on the fins of one or two fish. I guess your tank may be overstocked or the filter is not doing its job properly or you are not doing sufficient water changes. My advice is for you to do some water changes and also check the ammonia and nitrite levels in the tank. Then act appropriately by fixing whatever is causing the problem. Basic fish keeping rules are 1 inch of fish need a minimum of 1 gallon of water. Every occupied fish tank needs a cycled filter and at least 50% of a tanks water should be replaced weekly.